Drum-type percussion instruments, such as bass drums and the like, typically comprise a hollow cylindrical drum shell with a vibratory membrane or drum head stretched tightly over each end to define a resonant cavity within the shell. When a drum head is struck, it vibrates with a particular resonance, and this vibration is transmitted to the air within and outside of the cavity, as well as through the shell. The sum of these vibrations is perceived as the sounds produced by the drum.
Each of the drum heads has a larger diameter than the shell so that it may overlap the outer periphery of the shell and be secured against the periphery by a hoop or rim that fits tightly over the end of the shell. Typically, the rims are bolted or otherwise affixed to the drum shell, or to a bracket that is affixed to the shell. A disadvantage of this type of arrangement is that attachment of the rim to the shell, especially by use of securing bolts that pass through the shell wall, will adversely affect the quality of the sound produced by the drum.
With the passage of time and as a drum is play, the tension of the drum heads on the shell may change by stretching of the vibratory membrane or loosening of its attachment to the shell. This change in tension will affect the sound produced, and will make it necessary to adjust the tension in the membrane or "tune" the drum to obtain the desired degree of tension, and consequently, the desired sound which the drum can produce. Typically, this tuning of a drum head is accomplished by tightening the mechanism which attaches the drum head to the shell. It is not unusual for tuning of the drum heads to be required frequently throughout the useful life of the membrane.
Various drum head attachment and tuning mechanisms have been devised. Thus, for example, U.S. Pat. No. 4,154,136 of McIntyre describes a tension adjusting system for a drum that operates on a cam action principle. This system includes tension bands and tension adjusting mechanisms that are connected to the shell by a plurality of bolts. U.S. Pat. Nos. 4,570,526 and 5,208,412 of Hoshino, and U.S. Pat. No. 4,928,566 of Yanagisawa describe other types of tension application and adjusting mechanisms that are attached by means of brackets that are bolted onto and through the drum shell. Unfortunately, the securing bolts for these adjusting mechanisms or for the brackets to which they are attached pass through the shell wall, which adversely affects the quality of the sound produced by the drum. In addition, the application of tension forces at a plurality of points around the periphery of the vibratory membrane will serve to tension or tighten the membrane in a non-uniform manner, thus creating areas in the membrane that are in different states of tension, and therefore not in the same tune.
Recognizing the disadvantages inherent in attaching the tensioning and adjusting mechanisms through the shell wall of the drum, several systems have been developed for applying tension between the upper and lower rims along a plurality of external tension rods that are mounted between the rims, but are not attached through the wall of the drum shell. Among the systems of this type are those described in U.S. Pat. No. 4,334,458 of Grauso, U.S. Pat. No. 4,869,146 of Bonsor, U.S. Pat. No. 4,967,634 of Whynott, U.S. Pat. No. 5,410,938 of Kurosaki et al., U.S. Pat. No. 5,546,841 of Chen and European Patent Application Publication No. 0194834A2. Each of these systems includes upper and lower rims that project radially outwardly from the shell of the drum. Between these rims are mounted internally threaded tension rods which are attached to the upper and lower rims, or to auxiliary rims that are attached to the upper and lower rims, with bolts. By adjusting the depth of the upper and lower sets of bolts into the tension rods, tension is applied along the tension rods between the upper and lower rims. The application of tension between the upper and lower rims transmits tuning forces between the two rims. Thus, when the bolts through the upper rims are adjusted, not only is the tension in the upper drum head affected, but also the tension in the lower one. Furthermore, the application of tension forces at a plurality of opposed points around the peripheries of the vibratory membranes will also create areas in each of the membranes that are in different states of tension, and therefore not in the same tune. These effects make it quite difficult to properly tune and maintain the tension in both of the membranes of a drum equipped with one of these systems.
Although all of these tension rod systems operate according to the same general principles, they each include unique variations, as well. Thus, for example, the system of Grauso includes a suspension band to which each of the tension rods is bolted. This suspension band encircles the outer surface of the shell approximately midway between the top and bottom of the drum, and is provided with a spacer ring that fits within a channel in the outer surface of the shell. Although the tension application and adjusting mechanism of Grauso is not bolted to and through the shell, it does directly contact it, which contact would produce a deadening effect on the vibrations being transmitted through the shell as the drum is played. The system of Bonsor includes an intermediate hoop which is mounted atop the shell and bolted to the upper rim and to which the tension rods are attached. This system reportedly allows for some independent adjustment of the upper and lower membranes, but because the intermediate hoop is directly mounted on the shell, the transmission of vibrations through the shell wall will be adversely affected. The system of U.S. Pat. No. 5,410,938 of Kurosaki et al. employs a pair of suspension rings that are similar to the single intermediate hoop of Bonsor. Each of these rings is attached to the shell at one end and the tension rods are attached therebetween. The upper and lower rims are bolted to one of the suspension rings. However, because the suspension rings are directly mounted on the shell, the transmission of vibrations through the shell wall will be adversely affected.
U.S. Pat. No. 5,442,988 of Mayo also describes a drum with a tensioning and adjusting system that applies tension between the upper and lower rims. In this system, however, the tension is applied along a plurality of pairs of tension rods that are connected through adjustment mechanisms that are mounted on the side of the drum shell between the upper and lower rims. This adjusting mechanism comprises a nonreversing gear that is attached to a threaded cylinder. The nonreversing gear is turned by a worm gear or a pinion gear which is connected to a knob that extends from the side of the adjusting mechanism. Although this mechanism may provide advantages over the combination of bolts threaded into a tension rod at each end, it nevertheless transmits tension between the upper and lower rims. Furthermore, the adjusting mechanisms of Mayo are attached to the shell of the drum, which attachment will deaden the vibrations being transmitted through the shell as the drum is played.